During oil & gas exploration and production, especially for oil testing, downhole operation, oil & gas layer reconstruction, stratum testing, injection and production adjustment; temporary or permanent blocking to an oil/gas/water layer; using blocking tools is needed. In some cases, squeezing cement to block a perforated interval or channeling outside casing is also required for secondary cementing. A retrievable bridge plug is one retrievable blocking tool. When blocking is needed, the bridge plug is placed down to predetermined position, calibrating the depth, a setting controlled from ground, and temporary, permanent or selective blocking may be performed to the destination layer. Depending on the construction requirement, the retrievable bridge plug may be also used for a squeezing operation. Additionally, the retrievable bridge plug may be associated with other downhole tools to perform production well testing, oil/gas layer protection and snubbing, etc. A special releasing tool applies for retrieval of the bridge plug. Repeatable use of the bridge plug is possible after simple maintenance.
Chinese patent Patent Number 00 2 20245.x discloses a retrievable bridge plug which is sent in for setting by coiled tubing or a wire line. This bridge plug has full function and stable performance and may be associated with other downhole tools such as inserting slide bushing switch, but it can not be used for the squeezing operation, because the bridge plug can not be taken out after the cement hardens into concrete. A sleeving valve cement retainer referred to as “WSRA” manufactured by SIJISERVA (Hubei, Jingzhou) with a simple structure is low in cost and can be used for a secondary cement squeezing operation. However, there are disadvantages associated with the tool. First, this tool employs integral cast steel structure, which sometimes results in accidental jamming for the horizontal wells and high angle wells. Second, it sticks to the cement and results in unsuccessful release of the plug for squeezing cementing operation.